#include<iostream>
using namespace std;

class Person
{
public:
    void show_classname()
    {
        cout << "this is Person class" << endl;
    }

    void show_age()
    {
        if(NULL==this)
        {
            return;
        }
        m_age = 27;

        // cout << "the age is:" << this->m_age << endl;//注意m_age其实是 this->m_age;
        cout << "the age is:" << m_age << endl;
    }

    int m_age;
};

void test()
{
    Person *p = NULL;
    p->show_classname();
    p->show_age();

}

int main()
{
    test();

    return 0;
}